Page:EB1911 - Volume 25.djvu/117

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101
SILK

generations in the year and form reelable cocoons. Besides these there are many other mulberry-feeding Bombycidae in the East, principally belonging to the genera Theophila and Ocinara, the cocoons of which have not attracted cul- tivators. The moths yielding wild silks which have obtained most attention belong to the extensive and handsome

family Saturnidae. The most important of the species at the present time is the Chinese tussur or tasar worm, Antheraea pcrnyi (figs. 7, 8), an oak- feeding species, native of Mongolia, from which is derived the greater part of the so-called tussur silk nowimportedintoEurope. Closely allied to this is the Indian tussur moth (fig._ 9) Antheraea mylitla, found througliout the whole of India feeding on the bher tree, Zizyphus jujuba, and on many other plants. It yields a large compact cocoon (fig. 10) of a silvery grey colour, which Sir Thomas Wardle ol Leek, who devoted a great amount of attention to the wild-silk



Fig. 8. — Cocoon of Antheraea pernyi



Fig. 9. — Antheraea mylitla (female).


question, succeeded in reeling. Next in promising qualities the muga or moonga worm of Assam, Antheraea assama, a species to some extent domes- ticated in its native country. The yama-mai worm of Japan, Antheraea {Samia) yama-mai, an oak-feeder, is a race of considerable importance in Japan, where it was said to be jealously guarded against foreigners. Its eggs were first sent to Europe by Duchene du Bellecourt, French consul- general in Japan in 1861; but early in March following they hatched out, when no leaves, on which the larvae would feed were to be found. In April a single worm got oak-buds, on which it throve, and ultimately spun a cocoon whence a female moth issued, from which Guerin Meneville named and described the species. A further supply of eggs was secretly obtained by a Dutch physician Pompe van Meedervoort in 1863, and, as it was now known that the worm was an oak-feeder, and would thrive on the leaves of European oaks, great results were anticipated from the cultiva- tion of the yama-mai. These expectations, however, for various reasons, have been disappointed. The moths hatch out at a

Fl „ G ',, I0 '~ Coc ?° n of period when oak leaves are not ready Antheraea myhtta. for ^ feedJng) and the ^ . g ^

no means of a quality to compare with that of the common mulberry worm. The mezankoorie moth of the Assamese, Antheraea mezankooria, yields a valuable cocoon, as does also



IOI

the Atlas moth, Attacus atlas, which has an omnivorous larva found throughout India, Ceylon, Burmah, China and Java. The Cynthia moth, Attacus cynthia, is domesticated as a source of silk in certain provinces of China, where it feeds on the Ailan- thus glandulosa. The eria or arrindi moth of Bengal and Assam, Attacus ricini, which feeds on the castor-oil plant, yields seven generations yearly, forming loose flossy orange-red and some- times white cocoons. The ailanthus silkworm of Europe is a hybrid between A. cynthia and A. ricini, first obtained by Guerin Meneville, and now spread through many silk-growing regions. These are only a few of the moths from which silks of various usefulness can be produced; but none of these presents qualities, saving perhaps cheapness alone, which can put them in competition with common silk.

Physical and Chemical Relations of Silk. Common cocoons enclosing chrysalides weigh each from 16 to 50 grains, or say from 300 to 600 of small breeds and from 270 to 300 of large breeds to the lb. About one-sixth of this weight is pure cocoon, and of that one-half is obtainable as reeled silk, the remainder consisting of surface floss or blaze and of hard gummy husk. As the outer flossy threads and the inner vests are not reelable, it is difficult to estimate the total length of thread produced by the silkworm, but the portion reeled varies in length and thickness, according to the condition and robustness of the cocoon, in some breeds giving a result as low as 500 metres, and in others 900 to 1200 metres. Under favourable conditions it is estimated that n kilo- grammes of fresh cocoons give 1 kilogramme of raw silk for commerce, and about the same quantity "' for waste spinning purposes. Sir Thomas Wardle of Leek, in his handbook on silk published Fig. ii. — Microscopic appearance in 1887, showed by a series of Silk of chinese Tussur.

of measurements that the diameter of a single cocoon thread or bave varied from xrVirth to -frVtrth part of an inch in diameter in the various species of Bombycides, whilst those of the Saturnides or wild species varied from ^-^th to t ^ th part of an inch. As this estimation presents some difficulties and diver- gences, the size of the thread is generally defined commercially by deniers or decigrammes, those of the Anthereas (wild silks) being said to range from 5 to 8 deniers or decigrammes, results confirmed by actual experience with the reeled thread. The silk of the various species of Antheraea and Attacus is also thicker and stronger at the centre of the reeled portion than towards its extremities; but the diameter is much greater than that of common silk, and the filaments under the microscope (fig. n) present the appearance of flat bands, the exudation from the two spinnerets being joined at their flat edges. On this account the fibres of tussur or tussore silk tend to split up into fine fibrillae under the various preparatory processes in manufacturing, and its riband structure is the cause of the glassy lustre peculiar to the woven and finished fibres.

Silk fibre (see Fibres) consists essentially of a centre or core of fibroin, with a covering of sericin or silk albumen, and a little waxy and colouring matter. Fibroin, which is analogous to horn, hair and like dermal products, constitutes about 75 to 82 % of the entire mass, and has a composition represented by the formula Cut^NsOe. It has the characteristic appearance of pure silk — a brilliant soft white body with a pearly lustre — insoluble in water, alcohol and ether, but it dissolves freely in concentrated alkaline solutions, mineral acids, strong acetic acid and in ammoniacal solution of oxide of copper. Sericin, which constitutes the gummy covering (Fr. gres) of the fibre, is a gelatinous body which dissolves readily in warm soapy solutions, and in hot water, in which on cooling it forms a jelly with even as little as 1 % of the substance. It is precipitated from hot solutions by alcohol, falling as a white powder. Its formula is CisHzsNsOs. According to P. Bolley, the glands of the silkworm contain semi-liquid fibroin alone, and it is on exposure to the air that